This invention relates to a process for the production of acylamino acids in which the fatty acid halide is introduced into a circulation pipe provided with a mixer while the mixture of an amino acid and an alkali source is accommodated in the reactor, to the product obtained and to the use of these acylamino acids in surfactant-containing preparations.
N-acylamino acids, such as N-acyl glutamates for example, are known from the prior art as mild co-surfactants for use in cosmetic preparations. They are prepared by reaction of fatty acid chlorides with the amino group of glutamic acid sodium salt in the presence of bases, such as NaOH for example, in aqueous medium. The disadvantage of this process is that the lipophilic fatty acid chloride is difficult to react with the hydrophilic amino acid or the basic salt in aqueous medium. Attempts have been made to eliminate this problem by adding organic solvents such as, for example, acetone, methylethyl ketone, dioxane, polyols, tetrahydrofuran, t-butanol or cyclohexane.
Acylation in the absence of solvents, but using intensive stirring energy, is known from European patent EP 0827950 A1. The disadvantage of this process is the vigorous foaming by which it is accompanied so that the process is unsuitable for industrial application. This foaming can additionally lead to mixing problems where acid chloride or alkali is introduced. Accordingly, this process is not suitable for the production of acylamino acids on an industrial scale.
Patent application EP 0857717 A1 describes a process for the production of acylamino acids by reaction with fatty acid halides in the presence of water, alkali and polyols in conventional stirred tank reactors on the lines of a one-pot reaction. The disadvantages of this process lie in the sometimes very large quantities of polyol that are needed for an adequate yield and in the unsatisfactory mixing. The large polyol contents mentioned in the document in question are sometimes undesirable for the use of the resulting acylated amino acids. However, any reduction in the polyol content impacts adversely on the low-temperature behavior of the product.
Accordingly, the problem addressed by the invention was to provide a process for the production of acylamino acids which would guarantee uniform mixing of the reaction components without the foaming observed in traditional stirred reactors, and a product which would be distinguished by high stability at low temperatures and in storage.